NOAA-supported scientists
find large dead zone in Gulf of Mexico

August 4,
2011

NOAA-supported scientists
found the size of this year’s Gulf of Mexico dead zone to be 6,765 square
miles. Researchers had predicted the potential for a record sized dead
zone between 8,500 and 9,421 square miles due to the spring flooding of
the Mississippi River and the associated large loads of nutrients running
off into the Gulf, but strong winds and waves associated with Tropical
Storm Don disrupted the western portion of the dead zone.

The research cruise, led by
Nancy Rabalais, Ph.D., executive director of the
Louisiana Universities Marine Consortium, found this year’s dead zone
to be nearly equal to the land area of the state of New Jersey. The
average size of the dead, or hypoxic, zone over the past five years has
been 6,688 square miles, very close to this year’s measurement and much
larger than the 1,900 square mile goal set by the Gulf of
Mexico/Mississippi River Watershed Nutrient Task Force. Last year’s dead
zone measured approximately 7,722 square miles.

In addition to surveys in
the traditional region of the dead zone, Rabalais’ research team
documented a large area of hypoxia east of the Mississippi River in
mid-July.

“Although Tropical Storm
Don disrupted part of the hypoxic zone, our monitoring over the past
several months indicated the spring floods expanded the dead zone region,”
said Rabalais. “However, sampling the hypoxic bottom layer on a ship
rolling in 6-10 foot waves presented safety and sampling issues that
interfered with precise measurements at some stations. For these reasons,
the size of the measured hypoxic zone was smaller than just before the
storm, and is probably under-estimated.”

The dead zone is fueled by
nutrient runoff from agricultural and other human activities in the
Mississippi River watershed, which stimulates an overgrowth of algae that
sinks, decomposes and consumes most of the life-giving oxygen supply in
bottom waters. The hypoxic zone off the coast of Louisiana and Texas forms
each summer and threatens valuable commercial and recreational Gulf
fisheries.

These fisheries are
critical to the economy. For example, in 2009, the dockside value of
commercial fisheries in the Gulf was $629 million. Nearly three million
recreational fishers, taking 22 million fishing trips, further contributed
more than $1 billion to the Gulf economy.

“Despite fluctuations in
size due to each year’s weather conditions, these chronic, recurring
hypoxic zones every summer represent a significant threat to Gulf
ecosystems,” said Robert Magnien, Ph.D., director of
NOAA’s Center for Sponsored Coastal Ocean Research. “Until we achieve
a substantial reduction in nutrient pollution from the Mississippi River
watershed, we will continue to experience extended periods of time each
year when critically-needed habitat is unavailable for many marine
organisms.”

Earlier this summer,
NOAA-sponsored forecast models developed by R. Eugene Turner, Ph.D.,
Louisiana State University and Donald Scavia, Ph.D., University of
Michigan, predicted that the hypoxic zone would be the largest on record.
Despite the presence of tropical storms, which can temporarily provide
oxygen to bottom waters through mixing of the water column, the continued
high discharge from the Mississippi River after the prediction provided
strong conditions for a large dead zone.

The models used to forecast
the area of the dead zone are most influenced by the amount of May
nitrate-nitrogen delivered to the Gulf from the Mississippi and
Atchafalaya Rivers and are constructed to inform managers of the
underlying causes of the dead zone and the effectiveness of alternative
approaches to mitigate the problem over the long-term. These models
currently do not incorporate short-term variability due to weather
patterns that can affect the timing or positioning of the hypoxic zone in
any given year.

Prior to the Louisiana
Consortium cruise, a NOAA-supported Texas A&M survey, led by Steven
DiMarco, Ph.D., found a moderately sized dead zone during a June
shelf-wide survey, and subsequent measurements during NOAA’s Southeast
Monitoring and Assessment Program's summer survey indicated the dead zone
was growing larger in the areas that were likely re-oxygenated by Tropical
Storm Don. Texas A&M will be conducting a NOAA-funded follow-up cruise in
mid-August to provide an update on the size of the dead zone as scientists
work to understand size fluctuations and duration of hypoxic conditions in
the Gulf. The July cruise, however is the only survey mandated by the
Hypoxia Task Force to determine the annual extent of the dead zone.

NOAA’s mission is to
understand and predict changes in the Earth's environment, from the depths
of the ocean to the surface of the sun, and to conserve and manage our
coastal and marine resources.

Data compiled from The
British Antarctic Study, NASA, Environment Canada, UNEP, EPA and
other sources as stated and credited Researched by Charles
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